Communication: On the origin of the non-Arrhenius behavior in water reorientation dynamics

Guillaume Stirnemann (1, 2) , Damien Laage (1)

1 PASTEUR - Processus d'Activation Sélective par Transfert d'Energie Uni-électronique ou Radiatif (UMR 8640)
2 Department of Chemistry [New York]

We combine molecular dynamics simulations and analytic modeling to determine the origin of the non-Arrhenius temperature dependence of liquid water's reorientation and hydrogen-bond dynamics between 235 K and 350 K. We present a quantitative model connecting hydrogen-bond exchange dynamics to local structural fluctuations, measured by the asphericity of Voronoi cells associated with each water molecule. For a fixed local structure the regular Arrhenius behavior is recovered, and the global anomalous temperature dependence is demonstrated to essentially result from a continuous shift in the unimodal structure distribution upon cooling. The non-Arrhenius behavior can thus be explained without invoking an equilibrium between distinct structures. In addition, the large width of the homogeneous structural distribution is shown to cause a growing dynamical heterogeneity and a non-exponential relaxation at low temperature.

Domaines: Chimie théorique et/ou physique

Guillaume Stirnemann, Damien Laage. Communication: On the origin of the non-Arrhenius behavior in water reorientation dynamics. Journal of Chemical Physics, 2012, 137 (3), pp.031101. ⟨10.1063/1.4737390⟩. ⟨hal-01339396⟩